Physics Laboratory IExperiment: Radioactivity

Geiger Muller Counter& Radioactivity Simulation

(Dice Analogy)

What we’ll cover . . .

• What is Radiation?– Types– Characteristics

• Sources of Radiation• Concepts

– Radioactivity– Half-Life– Contamination vs. Exposure– Protection and Biological

Effects Dice analogy experiment

“Life on earth has developed with an ever present background of radiation. It is not something new, invented by the wit of man: radiation has always

been there.” Eric J Hall, Professor of Radiology, College of Physicians and Surgeons, Columbia University, New York, in his book Radiation and Life

Dünyadaki hayat, şimdiye dek mevcut arka-plan radyasyonu ile gelişti. İnsanoğlu tarafından icat edilen yeni bir şey değildir: radyasyon her zaman orada olmuştur.

Radiation

• Radiation is energy that comes from a source and travels through space and may be able to penetrate various materials.

Source: ESA/NASA/SOHOPublished: 26 August 2016

Types of Radiation

Radiation is classified into:

1) Ionizing radiation

2) Non-ionizing radiation

Non-ionizing Radiation

• Definition:

“They are electromagnetic waves incapable of producing ions while passing through matter, due to their lower energy.”

• Light, radio, and microwaves are types of radiationthat are called nonionizing.

Examples on Non-ionizing Radiation Sources

Visible light

Microwaves

Radios

Video Display Terminals

Power lines

Radiofrequency Diathermy

(Physical Therapy)

Lasers

MICROWAVE

GAMMA

ULTRA V

VISIBLE

INFRARED

TV

AMRF

Is non-ionizing radiation harmful?

The answer to this question depends on what dose and which severe radiation you will be exposed to….

Types of UV Radiation

Type Wavelength Effect

UV-A“Black light” Region

315-400 nm Little effect

UV-B 280-315 nm Skin cancer

possible

UV-C 100-280 nm Cornea damage

Visible radiation hazards

• Common sources: sun, all visible lamps

• Major damage likely only if intense beam is focused on the retina

• Eye usually registers pain before serious damage occurs

Infrared Hazards

• Major effect is burns

• Eye is not very sensitive so can be damaged if IR is intense

• Skin burns possible but usually avoided due to pain from heat before serious injury occurs

Radio-frequency and Microwave Hazards

• Sources include analytical instruments (e.g. NMR), cathode ray tubes (including oscilloscopes, TVs, and computer monitors), microwave ovens, and communications devices (e.g. cell phones)

• Biological effects to man uncertain

• Suggestion of sterility problems, birth defects and cataracts from microwaves

• Pacemakers (kalp-pilleri) are effected by microwaves

LASER HAZARDS

• LASER = Light Amplified by Stimulated Emission of Radiation

• Especially hazardous due to very narrow beam which can be very intense

• Lens of eye may concentrate energy onto retina by another 100,000 times

LASER HAZARDS (cont’d)

• Use minimum power laser possible for job

• Keep laser beam off or blocked when not in use

• Post warning signs when lasers are in use

• Never look directly at a laser beam or align it by sighting over it

• If possible, use laser in lighted room so that pupils will be constricted

• Do not depend on sunglasses for shielding.

• Make sure any goggles used are for the wavelength of the laser used and are of adequate optical density

Path of incoming solar radiation

A magnetosphere is the area of space near an astronomical object in which charged particles are controlled by that object's magnetic field. Near the surface of the object, the magnetic field lines resemble those of a magnetic dipole. Farther away from the surface, the field lines are significantly distorted by electric currents flowing in the plasma (e.g. in ionosphere or solar wind). When speaking about Earth, magnetosphereis typically used to refer to the outer layer of the ionosphere.

Magnetosphere

https://www.afad.gov.tr/kbrn/radyasyon-uyari-isaretleri

What is radioactivity?

Nuclear decay or radioactivity, is the process by which a nucleus of an unstable atom loses energy by emitting ionizing radiation.

A material that spontaneously emits this kind of radiation which includes the emission of alpha particles, beta particles, gamma rays and conversion electrons

Radioactive Elements

• Any element over atomic number 83 is radioactive.

• Radioactive materials have unstable nuclei (too few or too many neutrons).

• When an unstable nucleus decays, it breaks apart emitting particles and energy as it decays.

• Three types of nuclear radiation:Alpha particles

Beta particles

Gamma radiation electromagnetic wave

Who discovered radioactivity?

• In 1896, Henri Becquerel accidentally left pieces of uranium salt in a drawer on a photographic plate.

• When he developed the plate, he saw an outline of the uranium salt on it.

• He realized that it must have given off rays that darkened the film.

Who Discovered Radioactivity?

Antoine Henri Becquerel

• Worked with uranium.• Noticed phosphorescence

caused film exposure after leaving uranium in the sun.

• Noticed same thing happened on cloudy days.

Who’s the Famous “Madame” of Radiological Fame?

Marie Curie

• With her husband Pierre, discovered radium and coined the term “radioactive”

• First woman to win two Nobel Prizes

Who discovered radioactivity?

• Two years later Marie and PierreCurie discovered two new elements, Polonium and Radium, both radioactive.

Ionizing Versus Non-ionizing Radiation

Ionizing Radiation

– Higher energy electromagnetic waves (gamma) or heavy particles (beta and alpha).

– High enough energy to pull electron from orbit.

Non-ionizing Radiation

– Lower energy electromagnetic waves.

– Not enough energy to pull electron from orbit, but can excite the electron.

(i) Primordial RadionuclidesThat radionuclides that are present since the creation of earth and having long half-lives, e.g. 210Pb, 226Ra, K40

(ii) Cosmogenic RadionuclidesThat radionuclides that are produced in the upper atmosphere as a result of cosmic rays interaction with light particles (carbon, Nitrogen and Oxygen), e.g. C14, 7Be, 22Na, 32P, 32S

(iii)Anthropogenic RadionuclidesThat radionuclides that are produced as a result of man-made activities such as nuclear fuel fabrication, enrichment, nuclear power generation, nuclear accidents etc., e.g. 137Cs, 134Cs, 131I, 90Sr etc.

Sources of radioactivity

Ionizing radiation• Ionizing radiation is produced by unstable atoms. Unstable atoms

differ from stable atoms because unstable atoms have an excess of energy or mass or both. Radiation can also be produced by high-voltage devices (e.g., x-ray machines).

• Atoms with unstable nuclei are said to be radioactive. In order to reach stability, these atoms give off, or emit, the excess energy or mass. These emissions are called radiation.

• The kinds of radiation are electromagnetic (like light) and particulate (i.e., mass given off with the energy of motion). Gamma radiation and x rays are examples of electromagnetic radiation. Gamma radiation originates in the nucleus while x rays come from the electronic part of the atom. Beta and alpha radiation are examples of particulate radiation.

Primary Types of Ionizing Radiation

Alpha particles

Beta particles

Gamma rays (or photons)

X-Rays (or photons)

Neutrons

Types of Ionizing Radiation

Alpha ParticlesStopped by a sheet of paper

Beta ParticlesStopped by a layer of clothingor less than an inch of a substance (e.g. plastic)

Gamma RaysStopped by inches to feet of concreteor less than an inch of lead

RadiationSource

The penetrating power of radiation.

© 2003 John Wiley and Sons Publishers

Alpha ParticlesAlpha particles

(symbol α ) are a

type of ionizing radiation ejected by the nuclei of some unstable atoms. They are large subatomic fragments consisting of two protons and two neutrons.

Alpha Emitter Atomic Number

americium-241 95

plutonium-236 94

uranium-238 92

thorium-232 90

radium-226 88

radon-222 86

polonium-210 84

Beta ParticlesThere are many beta emitters:

tritiumcobalt-60strontium-90technetium-99iodine-129 iodine-131cesium-137

Beta particles are subatomic particles ejected from the nucleus of some radioactive atoms. They are equivalent to electrons. The difference is that beta particles originate in the nucleus and electrons originate outside the nucleus.

Gamma Rays

A gamma ray is a packet of electromagnetic energy--a photon. Gamma photons are the most energetic photons in the electromagnetic spectrum. Gamma rays (gamma photons) are emitted from the nucleus of some unstable (radioactive) atoms.

Gamma emitting radionuclides are the most widely used radiation sources. The three radionuclides by far most useful are: cobalt-60,cesium-137, technetium-99 m.

Physical

Radionuclide Half-Life Activity Use

Cesium-137 30 yrs 1.5 x 106 Ci Food Irradiator

Cobalt-60 5 yrs 15,000 Ci Cancer Therapy

Plutonium-239 24,000 yrs 600 Ci Nuclear Weapon

Iridium-192 74 days 100 Ci Industrial Radiography

Hydrogen-3 12 yrs 12 Ci Exit Signs

Strontium-90 29 yrs 0.1 Ci Eye Therapy Device

Iodine-131 8 days 0.015 Ci Therapy

Technetium-99m 6 hrs 0.025 Ci Imaging

Americium-241 432 yrs 0.000005 Ci Smoke Detectors

Radon-222 4 days 1 pCi/l Environmental

Examples of Radioactive Materials

https://www.nde-ed.org/EducationResources/CommunityCollege/RadiationSafety/theory/sources.htm

Source: National Council on Radiation Protection and Measurement Report 160 (2006)

The average American now receives 620 millirem of radiation per year

A Comparison of the Sources

• The radiation around us that comes from naturally occuring radioactive sources is called “background radiation”. It varies from place to place but in Hong Kong, we are typically exposed to 3 millisieverts of radiation each year. We would receive a higher dose if, for example, we needed medical treatment or diagnosis that involved radiation.

Natural background radiation

• The natural radiation energy between few KeV to MeV

from primordial radionuclides are called background

radiation.

• Background radiation is of terrestrial and extra-

terrestrial origin.

PLANTS

ATMOSPHERE

SOURCE (BEDROCK) MAN, ANIMALS

SOILS

• Background radiation is that ionizing radiation which is naturally and inevitably present in our environment. Levels of this can vary greatly. People living in granite areas or on mineralised sands receive more terrestrial radiation than others, while people living or working at high altitudes receive more cosmic radiation. A lot of our natural exposure is due to radon, a gas which seeps from the Earth's crust and is present in the air we breathe.

General Nuclear Medicine

Nuclear medicine is a branch of medical imaging that uses small amounts of radioactive material to diagnose or treat a variety of diseases

Gamma Radiation

No Offspring

(BIRTH CONTROL)

Insect Pest Control

Sterile

SterileWild

Preservation of food and agricultural product by radiation

An alternate method of food preservation by irradiation of X ray or gamma rays.

It is used to prolong the shelf life of many food and agricultural products, destroy bacteria and microorganisms in food (pre packed or bulk) and grains(rice, corn..).

The food exposed to controlled amount of ionizing radiation in shielded area for a specific time to achieve desirable objectives.

The sources are gamma rays from Cobalt 60 or Cesium 137, X-rays up to 5 MeV or electron accelerators up to 10 MeV.

Does the irradiation process make food radioactive?

Irradiation under controlled condition does not make food radioactive.

Irradiation involves passing the food through and allow to absorb desired radiation energy.

Radiation processing of food do not induce any radioactivity.

Food preservation

Onion and potato are irradiation by 0.05 to 0.15 kGy

Effect of gamma irradiation treatment in delay ripening

Pear delay in ripening and decaying of under ambient condition.

Peach after 7 days of ambient storage

• Nuclear Energy

– Albert Einstein showed us that energy and matter are the same thing, both are inter-convertible.

• E=mc2

– Using mass losses during nuclear reactions, one can calculate the energy change of a system.

• E=mc2

– There is a difference between the mass of the individual nucleons that make up a nucleus and the actual mass of the nucleus.

• This is called the mass defect of the nucleus.• The mass defect occurs as energy is released when nucleons

join to form a nucleus.

1879-1955

Nuclear Energy - HistoryIn 1917

Ernest Rutherford the father of nuclear physics, is credited

with splitting the atom.

In 1932John Cockcroft and Ernest Walton, attempted to split

the atomic nucleus by entirely artificial means, using a particle

accelerator to bombard lithium with protons, thereby producing two

helium nuclei.

Ernest Rutherford

Reference :Wikipedia

Nuclear Energy - HistoryIn 1932 James Chadwick discoveredthe neutron.

In 1934 nuclear fission was first experimentally

achieved by Enrico Fermi In Rome, when histeam bombarded uranium with neutrons.

In 1938, German chemists Otto Hahn and FritzStrassmann, along with Austrian physicists LiseMeitner and Otto Robert Frisch, conductedexperiments with the products of neutron-bombarded uranium.

Reference :Wikipedia

Nuclear Energy - History

In the United States - the first man-made reactor, known as Chicago Pile-1, which achieved criticality on December 2, 1942. This work became part of the Manhattan Project, which built large reactors at the Hanford Site to breed plutonium for use in the first nuclear weapons, which were used on the cities of Hiroshima and Nagasaki.

Atomic bombings of Hiroshima and Nagasaki

photo taken at ground level of Nagasaki bombing

Nuclear Energy

Electricity was generated for the first time by a nuclear reactor on December 20, 1951, at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW (the Arco Reactor was also the first to experience partial meltdown, in 1955).

Nuclear Energy

Russia's first nuclear power plant, and the first in the world to produce electricity, was the

5 MWe Obninsk reactor, in 1954.

Block control panel Obninsk nuclear power plant. Photo: Ilya Varlamov

AM-1 reactor was shut down in 2002.Photo: Alexander Belenky / BFM.ru

Nuclear Power Plants

In 2009, 15% of the world's electricity came from nuclear power, despite concerns about safety and radioactive waste management. More than 150 naval vessels using nuclear propulsion have been built.

NuclearPower Plants

Many countries remain active in developing nuclear power, including China, India, Japan and Pakistan. All actively developing both fast and thermal technology, South Korea and the United States, developing thermal technology only, and South Africa and China, developing versions of the PBMR(Pebble Bed Modular Reactor).

Nuclear Power PlantsThe World Nuclear Industry Status Report 2009 states that "even if Finland and France each builds a reactor or two, China goes for an additional 20 plants and Japan, Korea or Eastern Europe add a few units, the overall worldwide trend will most likely be downwards over the next two decades". With long lead times of 10 years or more, it will be difficult to maintain or increase the number of operating nuclear power plants over the next 20 years. The one exception to this outcome would be if operating lifetimes could be substantially increased beyond 40 years on average. This seems unlikely since the present average age of the operating nuclear power plant fleet in the world is 25 years.However, China plans to build more than 100 plants, while in the US the licenses of almost half its reactors have already been extended to 60 years, and plans to build more than 30 new ones are under consideration. Further, the U.S. NRC and the U.S. Department of Energy have initiated research into Light water reactor sustainability which is hoped will lead to allowing extensions of reactor licenses beyond 60 years, in increments of 20 years, provided that safety can be maintained, as the loss in non-CO2-emitting generation capacity by retiring reactors "may serve to challenge U.S. energy security, potentially resulting in increased greenhouse gas emissions, and contributing to an imbalance between electric supply and demand." In 2008, the International Atomic Energy Agency (IAEA) predicted that nuclear power capacity could double by 2030, though that would not be enough to increase nuclear's share of electricity generation.

Nuclear Power Plants• In the U.S., there are approximately 100 nuclear reactors,

producing a little more than 20% of the country’s electricity.

• Advantages– No fossil fuels are burned.

– No combustion products (CO2, SO2, etc) to pollute the air and water.

• Disadvantages– Cost - expensive to build and operate.

– Limited supply of fissionable Uranium-235.

– Accidents (Three Mile Island & Chernobyl)

– Disposal of nuclear wastes

Nuclear Reactors

In nuclear reactors the heat generated by the reaction is used to produce steam that turns a turbine connected to a generator.

The potential biological effects and damagescaused by radiation depend on the conditions of theradiation exposure.

The different kinds of radiation have different energy loss effects LET.

It is determined by: quality of radiation

quantity of radiation

received dose of radiation

exposure conditions (spatial distribution)

World Map of Nuclear reactors

Consumption energy in the world

Reference: IEA

70

Units of Measurement

• Effect of ionizing radiation is determined by:– Energy of radiation

– Material irradiated

– Length of exposure

– Type of effect

– Delay before effect seen

– Ability of body to repair itself

Units of Radioactivity• The Becquerel (Bq): Disintegration per second, dps

• The curie (Ci)

1 Ci = 37,000,000,000 Bq

so 1 mCi = 37 MBq; and 1 µCi = 37 kBq

• rem: Rem is the term used to describe equivalent or effective radiation dose.

• In the International System of Units, the Sievert (Sv) describes equivalent or effective radiation dose. One Sievert is equal to 100 rem.

Radiation dose

Absorbed doseThe amount of energy that cells absorb,

measured in grays (Gy).

1 gray = 1 joule absorbed per kg of tissue

Equivalent dose A measure of possible harm from radiation,

also taking account of the radiation type,

measured in sieverts (Sv).

Type of Radiation Factor

gamma rays 1

beta particles 1

neutrons & protons 10

alpha particles 20

UK annual average dose is 2.6 mSv.

Maximum allowable dose for employees is 20 mSv.

Health effects of radiation

Several things can happen when an ionising radiation

penetrates a cell:

• The cell is unaffected.

• The cell is damaged but is able to repair itself.

• The cell is killed.

• The cell’s DNA is damaged but remains able to reproduce itself, in

its modified form. This cell could become cancerous.

If a sex cell is hit, ionisation may cause a genetic mutation.

An analogy...

Here's a way to think about measures of radiation:

Imagine that you're out in a rainstorm.

• The amount of rain falling is measured in becquerels.

• The amount of rain hitting you is measured in grays.

• How wet you get is measured in sieverts.

Units of Radioactivity• The Becquerel (Bq): Disintegration per second, dps

• The curie (Ci)

1 Ci = 37,000,000,000 Bq

so 1 mCi = 37 MBq; and 1 µCi = 37 kBq

• rem: Rem is the term used to describe equivalent or effective radiation dose.

• In the International System of Units, the Sievert (Sv) describes equivalent or effective radiation dose. One Sievert is equal to 100 rem.

Units of radiation and radioactivity

• In order to quantify how much radiation we are exposed to in our daily lives and to assess potential health impacts as a result, it is necessary to establish a unit of measurement.

• The basic unit of radiation dose absorbed in tissue is the gray (Gy), where one gray represents the deposition of one joule of energy per kilogram of tissue (=1 J/kg).

• However, since neutrons and alpha particles cause more damage per gray than gamma or beta radiation, another unit, the sievert (Sv) is used in setting radiological protection standards.

A. Quantifying Radioactive Decay

Measurement of Activity in disintegrations per second (dps);

• 1 Becquerel (Bq) = 1 dps;

• 1 Curie (Ci) = 3.7 x 1010 dps;

• Activity of substances are expressed as activity per weight or volume (e.g., Bq/gm or Ci/l).

B. Quantifying Exposure and Dose

• Exposure: Roentgen 1 Roentgen (R) = amount of X or gammaradiation that produces ionization resulting in 1 electrostatic unit of charge in 1 cm3 of dry air. Instruments often measure exposure rate in mR/hr.

• Absorbed Dose: rad (Roentgen absorbed dose) = absorption of 100 ergs of energy from any radiation in 1 gram of any material; 1 Gray (Gy) = 100 rads = 1 Joule/kg; Exposure to 1 Roentgen approximates 0.9 rad in air.

• Biologically Equivalent Dose: Rem (Roentgen equivalent man) = dose in rads x QF, where QF = quality factor. 1 Sievert (Sv) = 100 rems.

Effects

Mide bulantısıYorgunluk

kusma

kanama

The radium dial painters

• Watch-dial painters - United States Radium factory in Orange,

New Jersey, around 1917 .

• The Radium Girls (4000) were female factory workers who

contracted radiation poisoning from painting watch dials

withself-luminous paint.

• They were used to tip (i.e., bring to the lips) their radium-laden brushes to achieve a fine point.

• Unfortunately this practice led to ingested radium, and many of the women died of sicknesses related to radiation poisoning.

• The paint dust also collected on the workers, causing them to “glow in the dark.”

• Some also painted their fingernails and teeth with the glowing substance.

85

Biological Effects of Ionizing RadiationExposure

• Somatic• Affects cells originally exposed

(cancer)• Affects blood, tissues, organs,

possibly entire body• Effects range from slight skin

reddening to death (acute radiation poisoning)

• Genetic– Affects cells of future

generations

– Keep levels as low as possible (wear lead)

– Reproductive cells most sensitive

Dr Manjunatha S, CCIS

Radioactivity – is it a health problem?

• The Alpha, Beta and Gamma particles all add energyto the body’s tissues. The effect is called the Ionizing Energy. It can alter DNA.

• Even though Alpha particles are not very penetrative if the decaying atom is already in the body (inhalation, ingestion) they can cause trouble.

Biological Effects: Mechanisms of Injury

Ionizing Radiation

Cell Death

Cell Damage

Repair Transformation

External Dose

Radiation DoseDose or radiation dose is a generic term for a measure of radiation exposure. In radiation protection, dose is expressed in millirem.

X-Ray

Machine

Image (film)

After

Radiation dose (single chest x

ray = 5-10 mrem).

Contamination

Contamination is the presence of a radioactive material in any place where it is not desired, and especially in any place where its presence could be harmful.

Yuck!

90

Basic Safety Factors• Keep exposures As Low As Reasonably

Achievable (ALARA)

– Time - Keep exposure times to a minimum

– Distance - Inverse square law: by doubling distance from a source, exposure is dec by a factor of 4

– Shielding – wear lead, use lead wall

Time, Distance, and Shielding

There are Three Factors That Affect Your Body’s Exposure to Radiation:

shieldingdistance

Time

Distance – Inverse Square Law

Shielding

Risk

• The statistical probability that personal injury will result from some action – smoking, speeding, extreme sports, ect.

– ionizing radiation exposure

Is Radiation Safe?

• Safer than normal risk associated with many activities encountered daily

97

Monitoring Instruments

• Personal monitoring:

– Film badges, bracelet, rings

– Pocket dosimeter

Radiation Detection Instruments

Geiger Counter Liquid Scintillation Counter

Photo by Karen SheehanPhoto by Carl Tarantino

• This is a beta-gamma probe, which can measure beta and gamma radiation in millirems per unit of time.

Geiger Muller Counter

• A Geiger–Müller counter, also called a Geiger counter, is a type of particle detector that measures ionizing radiation. It detects the emission of nuclear radiation — alpha particles, beta particles, and gamma rays— by the ionization produced in a low-pressure gas in a Geiger–Müller tube, which gives its name to the instrument.

• In wide and prominent use as a hand-held radiation survey instrument, it is perhaps one of the world's best-known radiation instruments.

Geiger Muller Counter• Geiger counter instruments

consist of two main elements; the Geiger-Müller tube, and the processing and display electronics.

• The radiation sensing element is an inert gas-filled Geiger-Müller tube (usually containing helium, neon, or argon with halogensadded) at a low pressure which briefly conducts electrical charge when a particle or photon of radiation makes the gas conductive by ionization.

• The tube has the property of being able to amplify each ionization event by means of the Townsend avalanche effect and produces an easily measured current pulse which is passed to the processing electronics.

Some Nuclear Disasters

Japanese Fukushima nuclear disaster (2011 ),

• Fukushima Daichi, March 11, 2011An 8.9 magnitude earthquake and subsequent tsunami overwhelmed the cooling systems of an aging reactor along Japan's northeast coastline. The accident triggered explosions at several reactors at the complex, forcing a widespread evacuation in the area around the plant.

• Japanese Fukushima nuclear disaster (2011 )shut down the nation's 54 nuclear power plants.

• 2013 repots - highly radioactive, with some 160,000 evacuees still living in temporary housing.

• Some land will be unfarmable for centuries.

• The difficult cleanup job will take 40 or more years cost tens of billions of dollars

https://www3.nhk.or.jp/nhkworld/en/news/20191103_02/?fbclid=IwAR1-8FGJxvnOd1P5QVjBEdb_gvEt-yYQveF02hRiPt-293Z891PiRSnpw5c

August 10. 1985, Russia, the Echo II class submarine suffered an explosion, sending a radioactive cloud of gas into the air. Ten sailors were killed in the incident and 49

people were observed to have radiation injuries.

The abandoned city of Prypiat, Ukraine, Chernobyl disaster, Russia (1986).

• Chernobyl, April 26, 1986The Chernobyl disaster is considered to be the worst nuclear power plant disaster in history. On the morning of April 26, 1986, reactor number four at the Chernobyl plant exploded. More explosions ensued, and the fires that resulted sent radioactive fallout into the atmosphere. Four hundred times more fallout was released than had been by the atomic bombing of Hiroshima.

• One of the worst nuclearaccidents till date.• The accident killed 30 people directly and damaged approximately $7 billion of property. • A study published in 2005 estimates that there will

eventually be up to 4,000 additional cancer deaths related to the accident among those exposed to significant radiation levels.

• Radioactive fallout from the accident was concentrated in areas of Belarus, Ukraine and Russia. Approximately 350,000 people were forcibly resettled away from these areas soon after the accident.

Mushroom cloud from the atomic explosion over Nagasaki, Japan rising 60,000 feet into the air on the morning of August 9, 1945.

• On August 6, 1945, the uranium-type nuclear weapon, code named "Little Boy" was detonated over Hiroshima with an energy of about 15 kilotons of TNT.

• Destroying nearly 50,000 buildings and killing approximately 70,000 people.

• On August 9, a plutonium-type nuclear weapon code named "Fat Man" was used against the Japanese city of Nagasaki with the explosion equivalent to about 20 kilotons of TNT.

• Approximately 35,000 people killed.

Research Questions

• What are theadvantages anddisadvantages of nuclear power plant?

• What is your opinion about having a nuclear power plant? Is it necessary?

Experiment

Radioactive decay• Radioactive decay is a stochastic (i.e. random)

process at the level of single atoms, in that, according to quantum theory, it is impossible to predict when a particular atom will decay.

• However, the chance that a given atom will decay never changes, that is, it does not matter how long the atom has existed.

• For a large number of atoms however, the decay rate for the collection can be calculated from the measured decay constants, and the half-lives of the nuclides calculated

Random decay

Radioactivity is a chance process.

• The chance of decay for each nucleus is constant with time,

independent of temperature, pressure, other physical conditions.

• The properties of random decay are best displayed if large

numbers of events are involved.

• The rate of decay is proportional to the number of undecayed

nuclei present.

• The half-life of a radioisotope is the average time for half the

nuclei present to decay (for the activity to fall to ½ its previous value).

We know that the popcorn will go ‘pop’, but we don’t

know exactly which kernel will pop at any given time.

Popcorn!

Half life and mean life

Half-life is the time required for half of the atoms of a radioactive material to decay to another nuclear form.

Mean life is average of all half lives

Half-life

equal ratios in equal times

– The rate of radioactive decay is expressed in terms of half-life

• The half-life of an element is the time required from one-half of its unstable nuclei to decay

• The half-life of an element is related to the ration of 0.693 to its radioactive decay constant

–t ½ = 0.693/k

• The decay constant for U238 is 4.87 X 10-18/s

• The half life is therefore

–t ½ = 0.693/4.87 X 10-18/s = 1.42 X 1017s = 4.5 X 109

years

• The half-life of U238 is 4.5 billion years.

• Radioactive decay of a hypothetical isotope with a half-life of one day. The sample decays each day by one-half to some other element. Actual half-lives may be in seconds, minutes, or any time unit up to billions of years.

Half Life Calculation

This experiment serves as an easily understood analogy for radioactive decay and for the more general case of first order kinetics. The shaking of one of the possible numbers on a certain type of dice corresponds to the nuclear state that results in radioactive decay.

The probabilistic nature of radioactive decay is clearly demonstrated.

Dice Analogy

• Dice rolling (Emeric, 1997) is a useful pedagogical tool (Arthur & Ian, 2012; Todd, Clifton, Ingrid, & Zdravko, 2006) to introduce students to the concepts and essential features of radioactivity.

• It can be ex-tended to explain radioactive branching. In the process, the students learn about half life, decay constant and activity of a radioactive substance. Terms like stochastic processes, probability.

This lab uses a simple analogy to show how the exponential law arises from the (random) decay probability of individual atoms.

We use a collection of six - sided dice as our "radioactive" atoms. Here's how the analogy works:

Think of the dice as atoms of a radioactive parent element. Each roll of the dice represents an increment of time, let's say, one year.

Dice that land on <1> are considered to have <decayed>.

We remove them from the population and record the number that survived.

Dice Analogy

Now we roll the remaining dice again (another "year" goes by). Again, we remove those that land on '6', note the number of surviving atoms, and roll them again. And so on ....

= 1/6 yr-1 = 0.1667 yr-1

References

• www.taek.gov.tr• https://www.nde-

ed.org/EducationResources/CommunityCollege/RadiationSafety/introduction/backround.htm• https://www.world-nuclear.org/information-library/current-and-future-generation/outline-history-

of-nuclear-energy.aspx• https://www.who.int/ionizing_radiation/about/what_is_ir/en/• https://www.who.int/topics/radiation_non_ionizing/en/